Blood pressure is one index for analyzing cardiovascular disease, and performing a risk analysis based on blood pressure is effective in preventing cardiovascular-related conditions such as stroke, heart failure, and myocardial infarction.
Thus far, diagnoses have been made using blood pressure (casual blood pressure) measured at medical institutions, such as during hospital visits, health checkups, and so on. However, recent research has shown that blood pressure measured at home (home blood pressure) is more useful in diagnosing cardiovascular disease than casual blood pressure. As a result, sphygmomanometers for use at home are becoming widespread.
Many household sphygmomanometers employ an oscillometric or microphone blood pressure measurement technique. In oscillometric blood pressure measurement, a measurement band (cuff) that contains an air bladder is wrapped around a measurement area such as an upper arm, the internal pressure of the cuff (a cuff pressure) is increased to a predetermined pressure (for example, 30 mmHg) beyond the systolic blood pressure, and a change in the volume of the artery is detected as a change in the pressure overlapping the cuff pressure (a pressure pulse wave amplitude) while the cuff pressure is reduced gradually or in steps; the systolic blood pressure and the diastolic blood pressure are determined based on the changes in the pressure pulse wave amplitude. Furthermore, with the oscillometric technique, it is possible to measure blood pressure by detecting a pressure pulse wave amplitude occurring while the cuff pressure is being increased.
Meanwhile, in the microphone technique, the cuff is wrapped around a measurement area such as the upper arm and the cuff pressure is increased to a predetermined pressure beyond the systolic blood pressure, in the same manner as with the oscillometric technique. Thereafter, the Korotkoff sound produced by the artery is detected by a microphone provided within the cuff as the cuff pressure is gradually reduced; the cuff pressure when the Korotkoff sound is produced is taken as the systolic blood pressure, whereas the cuff pressure when the Korotkoff sound is weak or is not present is taken as the diastolic blood pressure.
With either method, if the cuff of the sphygmomanometer is not properly wrapped around the measurement area, the cuff pressure will not be sufficiently transmitted to the artery, resulting in a drop in the measurement accuracy. Accordingly, with respect to a sphygmomanometer having a configuration that automatically wraps a cuff around a measurement area (called a “fully-automatic arm sphygmomanometer” hereinafter), the present applicants have, in JP 2005-230175A (Patent Literature 1), previously disclosed a technique in which a curler configured of a flexible member and a wrapping air bladder are disposed on the outside of a measurement air bladder for wrapping the measurement air bladder around the measurement area; by inflating the wrapping air bladder, the diameter of the curler is reduced, thus wrapping the measurement air bladder around the measurement area.
Furthermore, the present applicants have, in JP 2009-279196A (Patent Literature 2), previously disclosed a technique for improving the accuracy of oscillometric blood pressure measurement; with this technique, the measurement accuracy is improved by reducing skew in a detected pressure pulse wave amplitude through control that brings an air exhaust flow amount from a measurement air bladder per unit of time into a proportional relationship with a speed of deflation of the measurement air bladder.